missing feature dependency: 9

[grunch]

I'm trying to pay a phoenix invoice from my lnd node but I get this message

{
    "payment_error": "missing feature dependency: 9",
    "payment_preimage": null,
    "payment_route": null,
    "payment_hash": "ad65903688e74100028a95814fc7b1e1f41d8441deaa278c2588998c13c03940"
}

According with lalou the invoice is missing the onion tlv, which is needed in order to use mpp.

And in fact if I decoded the phoenix invoice I don't see feature 9 tlv-onion

    "features": {
        "15": {
            "name": "payment-addr",
            "is_required": false,
            "is_known": true
        },
        "17": {
            "name": "multi-path-payments",
            "is_required": false,
            "is_known": true
        },
        "51": {
            "name": "unknown",
            "is_required": false,
            "is_known": false
        }
    }

[t-bast]

This is a known issue and will be fixed in the next release (fixed here: ACINQ/eclair#1253).
The spec explicitly disallowed var_onion_optin in invoices, which is why we left it out.
There is a pending PR on the spec to add this feature bit which should be merged soon: lightning/bolts#719